Retention mechanism, driving apparatus, and blur correction apparatus

ABSTRACT

A retention mechanism includes a fixed part including a magnet, and a movable part opposed to the fixed part. A plurality of rolling elements are provided between the fixed part and the movable part, and the movable part is movable in a plane direction. A magnetic material which forms, in combination with the magnet, a magnetic spring is provided on the movable part. The magnetic spring generates a magnetic attraction force which attracts the movable part to the fixed part. The magnetic material is extended along a direction in which magnetic poles of the magnet are arrayed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional application of U.S. Ser. No. 14/321,327, filed Jul. 1, 2014, which is based upon and claims the benefit of priority from Japanese Patent Application No. 2013-189877, filed Sep. 12, 2013, and No. 2013-189878, filed Sep. 12, 2013; the entire contents of all of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a retention mechanism which holds a movable part movable in a plane direction perpendicular to an array direction thereof in relation to a fixed part, a driving apparatus which moves the movable part in the plane direction in relation to the fixed part, and a blur correction apparatus using the retention mechanism and/or the driving apparatus.

BACKGROUND

Conventionally, as a blur correction apparatus, there is an known apparatus which corrects a camera shake by moving a movable part holding a lens or an imaging element (optical member) of a camera along a plane perpendicular to an optical axis in relation to a fixed part.

This type of blur correction apparatus generally comprises a plurality of balls as a spacer which is arranged between a movable part and a fixed part, a plurality of coil springs which draw and tension the movable part toward the fixed part so as to sandwich the plurality of balls in the optical axis direction, and two sets of voice coil motors (VCMs) which move the movable part in the plane direction in relation to the fixed part.

The VCM ordinarily comprises a magnet provided on one of the movable part and the fixed part, a coil provided on the other one of the movable part and the fixed part, and at least one yoke which forms a magnetic circuit in combination with the magnet and the coil. The yoke is provided on at least one of the movable part and the fixed part.

Another retention mechanism is also known which uses a magnetic spring to attract and hold the movable part to the fixed part, in place of providing a plurality of coil springs. As an example of the magnetic spring, there is a known configuration in which a movable part is attracted to a fixed part by using a magnetic attraction force between a magnet provided on the movable part (or fixed part) and a yoke provided on the fixed part (or movable part), to hold the movable part between both parts (for example, Jpn. Pat. Appln. KOKAI Publication No. 2013-88684). That is, when such a magnetic spring is used, no coil spring is required and the apparatus configuration can be simplified accordingly.

However, in an apparatus using this type of magnetic spring, there is a difficulty in obtaining appropriate magnetic attraction force of magnification for holding a movable part at a fixed part without spoiling an original function (i.e., the function to improve output of the VCM). It is therefore difficult to simultaneously perform both functions satisfactorily.

Since the yoke ordinarily has a size substantially equal to a magnet, the magnetic attraction force which is generated in combination with the magnet is greater, compared with the attractive force of a coil spring when this kind of magnetic spring is used. Therefore, the force with which a plurality of balls are sandwiched in an optical axis direction becomes excessive, and the movable part and fixed part tend to be easily worn out and degraded due to sliding contact with the balls.

Also, when this type of magnetic spring is used, a magnet or a yoke needs to be provided on the movable part. In any case, the movable part is heavy, and power consumption of the VCM therefore increases.

The present invention has been made in view of circumstances as described above and has an object of providing a retention mechanism capable of attracting a movable part toward a fixed part with appropriate force, a driving apparatus capable of efficient stable operation without an increase in weight of the movable part, and a blur correction apparatus using the retention mechanism and/or the driving apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is sectional view of a camera according to an embodiment;

FIG. 2 is an enlarged sectional view showing a vibration-proof unit built in the camera in FIG. 1, according to the first embodiment;

FIG. 3 is a perspective view of the vibration-proof unit in FIG. 2, viewed from an oblique front side;

FIG. 4 is an exploded perspective view of the vibration-proof unit in FIG. 3;

FIG. 5 is an exploded perspective view of the vibration-proof unit in FIG. 3, viewed from an oblique rear side;

FIG. 6 is an exploded perspective view of a movable part of the vibration-proof unit in FIG. 3;

FIG. 7 is a block diagram of a control system which controls operation of the movable part of the vibration-proof unit in FIG. 2;

FIG. 8 is a front view showing a vibration-proof unit according to the second embodiment;

FIG. 9 is a front view of the movable part of the vibration-proof unit in FIG. 8 wherein a yoke is removed;

FIG. 10 is a front view showing the vibration-proof unit in FIG. 3 in which a yoke is shown in dot line;

FIG. 11 is an enlarged partial sectional view showing the vibration-proof unit in FIG. 10 which is cut along F11-F11;

FIG. 12 includes a front view (a) and a side view (b), showing a relationship between a magnet and a coil of the vibration-proof unit in FIG. 3;

FIG. 13 shows an intensity distribution of magnetic flux along a driving direction in FIG. 12;

FIG. 14 shows an intensity distribution of magnetic flux along a cross-driving direction in FIG. 12;

FIG. 15 is an operation view for explaining behaviors of a magnetic material provided on the movable part of the vibration-proof unit in FIG. 3;

FIG. 16 is an operation view for explaining, together with FIG. 15, behaviors of the magnetic material provided on the movable part of the vibration-proof unit in FIG. 3;

FIG. 17 is a graph showing a relationship between movement of the magnetic material in FIG. 16 and a restoring force which acts on the magnetic material;

FIG. 18 is a view for explaining appropriate dimensions of the magnetic material provided on the movable part of the vibration-proof unit in FIG. 3;

FIG. 19 is a side view of FIG. 18; and

FIG. 20 is a view showing a modification when a coil is provided on a movable part.

DETAILED DESCRIPTION

Hereinafter, embodiments of the invention will be described with reference to the drawings.

FIG. 1 is a sectional view of a camera 100 according to an embodiment. In descriptions below, a direction from the right to the left is supposed to face the front side, and the opposite direction thereof is supposed to face the rear side. Further, an axis corresponding to the optical axis O of the camera is supposed to be the Z-axis (axis in longitudinal directions). Two axes which are perpendicular to each other along a plane perpendicular to the Z-axis are supposed to be the Z-axis (horizontal axis) and the Y-axis (vertical axis).

The camera 100 comprises a lens unit 12, a shutter unit 14, a vibration-proof unit 10, and a display unit 16. The camera 100 comprises a case 18 which stores a plurality of units 12, 14, 10, and 16 arrayed in the direction of optical axis O (array direction). The vibration-proof unit 10 is an example of a driving apparatus and a blur correction apparatus.

The lens unit 12 forms an image of an unillustrated object onto an imaging element 1 (a driven member or an optical member) provided on the vibration-proof unit 10. The shutter unit 14 controls the time to expose the object to the imaging element 1 by controlling the opening/closing time. The vibration-proof unit 10 moves the imaging element 1 along a plane perpendicular to the optical axis O so that an image may not be blurred even when the camera 100 is vibrated at the time of photographing. The display unit 16 is provided on the back side of the case 18, and displays a digital image photoelectrically converted with the imaging element 1.

Hereinafter, the vibration-proof unit 10 according to the first embodiment will be described with reference to FIGS. 2, 3, 4, 5, and 6.

FIG. 2 is an enlarged sectional view of the vibration-proof unit 10 in FIG. 1. FIG. 3 is a perspective view of the vibration-proof unit 10 viewed from an oblique right front upper side. FIG. 4 is an exploded perspective view of the vibration-proof unit 10 viewed from an oblique front side thereof. FIG. 5 is an exploded perspective view of the vibration-proof unit 10 viewed from an oblique rear side thereof. FIG. 6 is an exploded perspective view of a movable part of the vibration-proof unit 10.

The vibration-proof unit 10 comprises: a fixed frame 2 (fixed part or first fixed part) to which two first magnets 2 a and 2 b for driving in the X-axis direction and a second magnet 2 c for driving in the Y-axis direction; a movable part 40 in which two first coils 4 a and 4 b for driving in the X-axis direction, a second coil 4 c for driving in the Y-axis direction, and the imaging element 1 are fixed to a movable frame 4; and a yoke 6 (second fixed part, first yoke, or second yokes) made of a metal plate, such as SPCC or SUS304.

As shown in FIG. 4, the first magnet 2 a is attached to an upper left corner part of a front surface of the fixed frame 2 having an approximately rectangular plate shape. More specifically, the first magnet 2 a is adhered to the front surface of the fixed frame 2 by an adhesive agent with the two yokes 21 layered on each other and sandwiched between the magnet and the surface. The first magnet 2 a is adhered to the fixed frame 2 in a posture in which a direction in which the magnetic poles thereof are arrayed is parallel to the X-axis.

The other first magnet 2 b is adhered, in a similar manner to the above, to a left lower corner part of the front surface of the fixed frame 2 (apart from and below the first magnet 2 a in the figure) with the two yokes 21 sandwiched between the magnet 2 b and the corner part. The first magnet 2 b is also attached to the fixed frame 2 in a posture in which a direction in which magnetic poles thereof are arrayed is parallel to the X-axis, like the first magnet 2 a.

Further, the second magnet 2 c is arrayed in relation to the first magnet 2 b in the X-axis direction along a lower edge of the front surface of the fixed frame 2. The second magnet 2 c is also adhered to the front surface of the fixed frame 2 with the two yokes 21 sandwiched between the magnet 2 c and the surface. Further, the second magnet 2 c is attached to the fixed frame 2, directed in a manner that a direction in which magnetic poles thereof are arrayed is parallel to the Y-axis, i.e., directed in a direction which differs by 90 degrees from the direction in which the magnetic poles of each of the first magnets 2 a and 2 b are arrayed.

As shown in FIGS. 4 and 5, three coils 4 a, 4 b, and 4 c attached to the movable frame 4 are laid out at positions respectively opposed to the three magnets 2 a, 2 b, and 2 c of the fixed frame 2 where the vibration-proof unit 10 is assembled with the movable frame 4 opposed to the fixed frame 2 (for example, a state of FIG. 3). As shown in FIG. 6, each of the coils 4 a, 4 b, and 4 c is stored and positioned in a counter-bored part (not shown) formed in a rear surface of the movable frame 4 and is fixed thereto by an adhesive agent.

The two first coils 4 a and 4 b each are attached to the movable frame 4 in such a direction in which the coils 4 a and 4 b can move the movable frame 4 in the X-axis direction (first direction) in relation to the fixed frame 2 by an electromagnetic induction effect in combination with the respectively opposed first magnets 2 a and 2 b when a control current is made to flow through the coils 4 a and 4 b. The second coil 4 c is attached to the movable frame 4 in such a direction in which the second coil 4 c can move the movable frame 4 in the Y-axis direction (the second direction) in relation to the fixed frame 2 by the electromagnetic induction effect in combination with the opposed second magnet 2 c when a control current is made to flow. By changing directions of the currents made to flow through the coils 4 a, 4 b, and 4 c, the moving direction of the movable frame 4 can be switched to the opposite direction.

As shown in FIG. 6, an imaging element 1, a heat sink 42, a filter assembly 43, and a filter retainer frame 44 are further attached to the movable frame 4. The movable frame 4 comprises a substantially rectangular mount hole 41 to allow the imaging element 1 to be attached. The imaging element 1 is attached to the mount hole 41 from the rear side of the movable frame 4. The heat sink 42 is attached in contact with a rear surface of the imaging element 1.

The filter assembly 43 has a structure in which optical filters, such as an optical low pass filter and an infrared ray cut filter, are layered in the optical axis direction. The filter retainer frame 44 is arranged in the front side of the filter assembly 43 and is fixed to the movable frame 4 with a screw. In this manner, the filter assembly 43 is attached to the movable frame 4.

In a front surface of the movable frame 4, three elongated narrow counter-bored parts 41 a, 41 b, and 41 c are provided to respectively store and arrange the two first magnetic materials 5 a and 5 b and a second magnetic material 5 c. That is, the three magnetic materials 5 a, 5 b, and 5 c are also movable together with the movable frame 4.

The counter-bored parts 41 a and 41 b for attaching the two first magnetic materials 5 a and 5 b are provided in the side opposite to the counter-bored parts of the first coils 4 a and 4 b, respectively, and are extended in the X-axis direction. That is, the two first magnetic materials 5 a and 5 b are opposed also to the two first magnets 2 a and 2 b in the side of the fixed frame 2 where the vibration-proof unit 10 is assembled. The two first magnetic materials 5 a and 5 b are extended respectively along array directions (first directions) of the poles of the respectively opposed magnets 2 a and 2 b, and areas of the two first magnetic materials projected onto the first magnets 2 a and 2 b fall within outer peripheral parts of the first magnets.

Conversely, the counter-bored part 41 c for attaching the second magnetic material 5 c is provided in the side opposite to the counter-bored part of the second coil 4 c and is extended in the Y-axis direction. That is, the second magnetic material 5 c is opposed also to the second magnet 2 c in the side of the fixed frame 2 where the vibration-proof unit 10 is assembled. The second magnetic material 5 c is extended along the array direction (second direction) of the poles of the opposed second magnet 2 c, and an area of the second magnetic material 5 c projected onto the second magnet 2 c falls within an outer peripheral part of the second magnet 2C.

As shown in FIG. 3, the yoke 6 has an approximately U-shaped structure so as to cover the three magnets 2 a, 2 b, and 2 c of the fixed frame 2 where the vibration-proof unit 10 is assembled. The yoke 6 is tightened and fixed to corresponding boss parts 22 on the side of the fixed frame 2 with use of three screws 6 a.

That is, the yoke 6 according to the present embodiment is configured by integrally connecting the first yoke which overlaps the first magnets 2 a and 2 b and the first coils 4 a and 4 b, and the second yoke which overlaps the second magnet 2 c and the second coil 4 c. The yoke 6 itself functions as a second fixed part which is fixed to the fixed frame 2.

In the present embodiment, as described above, a sheet of plate-type yoke 6 is directly fixed to the fixed frame 2. However, the yoke 6 may alternatively be divided into a plurality of pieces, and may be attached to another unillustrated fixed frame (second fixed part) which is fixed to the fixed frame 2.

In any case, the first magnets 2 a and 2 b, the first coils 4 a and 4 b, and the yoke 6 function as two voice coil motors (VCM) (first driving unit) which moves the movable frame 4 in the X-axis direction in relation to the fixed frame 2. The second magnet 2 c, the second coil 4 c, and the yoke 6 function as another voice coil motor (VCM) (second driving unit) which moves the movable frame 4 in the Y-axis direction in relation to the fixed frame 2.

When the vibration-proof unit 10 having the structure described above is assembled, three balls 3 a, 3 b, and 3 c (rolling elements) (refer to FIG. 4) are inserted to be sandwiched between the fixed frame 2 and the movable frame 4. Rectangle recesses 32 and 34 (refer to FIG. 11) to store the three balls 3 a, 3 b, and 3 c each are provided in the front surface of the fixed frame 2 and in the rear surface of the movable frame 4, respectively. Bottom plates 33 and 35 (refer to FIG. 11) to suppress abrasion with the balls 3 a, 3 b, and 3 c are provided at the bottoms of the recesses 32 and 34, respectively.

The movable part 40 is provided to be movable, floating from the fixed frame 2 (and the yoke 6). The movable part 40 is energized toward the fixed frame 2 by a magnetic attraction force which acts between the three magnetic materials 5 a, 5 b, and 5 c provided on the movable frame 4 and the three magnets 2 a, 2 b, and 2 c provided on the fixed frame 2. Therefore, the three balls 3 a, 3 b, and 3 c are held pinched by the recess 32 of the fixed frame 2 and the recess 34 of the movable frame 4 with the magnetic attraction force and function as a spacer therebetween.

That is, the first magnetic material 5 a and first magnet 2 a function as a first magnetic spring. The first magnetic material 5 b and the first magnet 2 b function also as a first magnetic spring. The second magnetic material 5 c and the second magnet 2 c function as a second magnetic spring. Structures and functions of the magnetic springs will be described in detail later.

The three sets of magnetic springs are provided respectively at positions of VCMs (the positions of the magnets 2 a, 2 b, and 2 c) and do therefore not always form a well-balanced layout due to relationships with supporting positions by three balls 3 a, 3 b, and 3 c. Therefore, according to the present embodiment, a coil spring 7 is attached to be bridged between the fixed frame 2 and the movable frame 4, in addition to the three magnetic springs.

As shown in FIG. 4, the ball 3 a is provided below the first magnet 2 a in the figure. The ball 3 b is provided between the first magnet 2 b and the second magnet 2 c. The ball 3 c is provided near the coil spring 7. That is, the three balls 3 a, 3 b, and 3 c support, at three points, the movable frame 4 in relation to the fixed frame 2.

In contrast, the three sets of magnetic springs are arranged at the positions of the VCMs as described above. The force of pulling the movable frame 4 toward the fixed frame 2 therefore comparatively weakens near the ball 3 c. According to the present embodiment, the coil spring 7 is therefore provided at this position. An end of the coil spring 7 is attached to the movable frame 4, and the other end of the coil spring 7 is attached to the fixed frame 2.

FIG. 7 is a block diagram of a control system which controls operation of the vibration-proof unit having a structure as described above.

The control system of the vibration-proof unit 10 comprises an X-axis gyroscope 102 and a Y-axis gyroscope 104 for detecting a blur amount of the camera 100, hall elements 106 and 108 for detecting the position of the imaging element 1 along the XY-plane of the imaging element 1, a vibration-proof control circuit 110 which calculates a blur correction amount from the detected blur amount and the position in plane directions, and an actuator driving circuit 112 which causes a drive current to flow through the coils 4 a, 4 b, and 4 c of each of the VCMs.

As described above, according to the present embodiment, the three magnetic materials 5 a, 5 b, and 5 c opposed respectively to the magnets 2 a, 2 b, and 2 c are provided on the movable frame 4, separately from the yoke 6 which forms the magnetic circuits of the VCMs. Separately from the magnetic circuit of the vibration-proof unit 10, functions as magnetic springs can be implemented so that the movable frame 4 can be attracted toward the fixed frame 2 with desired appropriate magnetic attraction force F. That is, the magnetic attraction force F can be easily controlled to a desired value by changing the areas of the magnetic materials 5 a, 5 b, and 5 c projected onto the magnets 2 a, 2 b, and 2 c and by changing thicknesses and materials of the magnetic materials 5 a, 5 b, and 5 c.

Also, according to the present embodiment, the magnetic materials 5 a, 5 b, and 5 c which are formed of comparatively small light plate pieces are provided on the movable frame 4. Therefore, in comparison with a case of providing a yoke on a conventional movable part, the weight of the movable part 40 can be lightened, and power consumption of the VCMs can be reduced. Further, a number of magnetic springs are used as mechanisms for attracting the movable frame 4 to the fixed frame 2 according to the present embodiment. Therefore, when the movable frame 4 is moved in the plane direction perpendicular to the optical axis O by blur correction operation, it is possible to reduce a force (restoring force along the XY-plane directions of each magnetic spring) acting to return the movable frame 4 to an original position before the movable frame 4 is moved, and undesirable load in the plane directions can be reduced at the time of blur correction.

Conversely, if a retention structure is employed in which the movable frame 4 is attracted to the fixed frame 2 only by magnetic springs, there is a possibility that the movable frame 4 vibrates greatly beyond an amplitude intended by the control when a control current having a frequency component corresponding to a resonance frequency specific to the vibration-proof unit 10 is made to flow through the coils 4 a, 4 b, and 4 c. Consequently, there can be a drawback that a long time is needed until vibration attenuates. Therefore, the coil spring 7 which mechanically attracts the movable frame 4 to the fixed frame 2 is provided to allow the drawback as described above due to resonance to be suppressed by control.

Also as described above, if the coil spring 7 is provided so as to compensate for a magnetic attraction force of the magnetic springs provided only at the positions of the VCMs, the balance of force in the Z-axis direction in the XY-plane can be improved excellently, and the vibration-proof unit 10 can be operated stably. Further, assemblability of the vibration-proof unit 10 can be greatly improved by providing not only magnetic springs but also the coil spring 7.

However, the configuration of coil spring 7 is not mandatory in the present invention. Insofar as the drawback due to resonance can be solved, the single coil spring 7 may be replaced with a magnetic spring. Alternatively, the coil spring 7 may be simply omitted.

FIG. 8 is a front view of a vibration-proof unit 50 according to the second embodiment without a coil spring 7, viewed from a front side along an optical axis O. FIG. 9 is a front view of the vibration-proof unit 50 of FIG. 8 from which a yoke 51 is removed. Here, components which function in the same manner as the vibration-proof unit 10 according to the first embodiment described above will be denoted with the same reference signs as in the first embodiment, and detailed descriptions thereof will be omitted herefrom.

The vibration-proof unit 50 according to the present embodiment comprises a fourth magnetic spring at the position to which the coil spring 7 is attached in the first embodiment. The fourth magnetic spring comprises an elongated narrow plate-type magnetic material 5 d extending in the X-axis direction, as shown in FIG. 9. The magnetic material 5 d is fixed to a front surface of a movable frame 4 in the same manner as other magnetic materials 5 a, 5 b, and 5 c. Further, an unillustrated magnet specialized only for a magnetic spring is adhered to a front surface of a fixed frame 2 opposed to the magnetic material 5 d. This magnet is provided in a posture in which a direction in which magnetic poles thereof are arrayed extends along the X-axis.

With respect to the fourth magnetic spring, magnetic attraction force F can also be controlled to a desired arbitrary value by changing an area of the magnetic material 5 d projected onto an opposed magnet and by changing a thickness in a Z-axis direction, as in the other three magnetic springs described above.

As described above, according to the second embodiment, only magnetic springs are used as a retention mechanism of the movable part 4 without using a coil spring 7. Therefore, undesirable force (force acting to return the movable part 4 to a neutral position) along the XY-plane, which is applied to the movable part 4 at the time of blur correction operation, can be reduced, and the power consumption of VCMs can be accordingly reduced.

Also according to the present embodiment, only magnetic springs are used, and therefore, an installation space thereof can be reduced more in comparison with a case of using the coil spring 7. Accordingly, the apparatus configuration can be more compact, which contributes to miniaturization of the apparatus.

Further, if only magnetic springs are used as in the present embodiment, friction noise which can be generated at two ends of a coil spring 7 when the coil spring 7 is used can be eliminated. Accordingly, convenience for users can be improved.

Hereinafter, the structure and function of magnetic springs in each of the foregoing embodiments will be described in more detail with reference to FIGS. 10 and 11. FIG. 10 is a front view of the vibration-proof unit 10 in the first embodiment viewed from the front side along the direction of optical-axis O. FIG. 11 is a sectional view partially taken along F11-F11 in FIG. 10. Since three magnetic springs function similarly, only the magnetic spring including the magnetic material 5 b will now be described as a representative, and descriptions of the other magnetic springs will be omitted herefrom. In FIG. 10, a yoke 6 is drawn with broken lines, in order to show the position and direction of the magnetic material 5 b in the XY-plane.

As shown in FIG. 11, a ball 3 b (3 a and 3 c) is provided between a movable frame 4 holding a coil 4 b (4 a and 4 c) and a magnetic material 5 b (5 a and 5 c) and a fixed frame 2 holding a magnet 2 b (2 a and 2 c). A recess 32 to receive the ball 3 b is provided in a front surface of the fixed frame 2, and a bottom plate 33 is provided on the bottom of the recess 32. A recess 34 to receive the ball 3 b is provided in a rear surface of the movable frame 4, and a bottom plate 35 is provided at the bottom of the recess 34.

The distance between a surface of the bottom plate 33 with which the ball 3 b has point-contact and the front surface of the fixed frame 2, and the distance between a surface of the bottom plate 35 with which the ball 3 b has point-contact and the rear surface of the movable frame 4 are set to values which are added to become smaller than the diameter of the ball 3 b. Therefore, a gap is formed between the front surface of the fixed frame 2 and the rear surface of the movable frame 4 which are opposed to each other with the ball 3 b inserted between each other. By providing a gap as described above, the movable frame 4 is made to float from the fixed frame 2, and the movable frame 4 is made movable along the XY-plane. When the movable frame 4 moves in a plane direction in relation to the fixed frame 2, the ball 3 b rolls inside the recesses 32 and 34.

At the position opposed along the direction of optical-axis O to the first magnet 2 b fixed to the front surface of the fixed frame 2, the first coil 4 b, first magnetic material 5 b, and yoke 6 are arranged, layered on each other in this order. The first coil 4 b is stored and arranged in and fixed to a counter-bored part formed in the rear surface of the movable frame 4. The first magnetic material 5 b is stored and arranged in and fixed to a counter-bored part 41 b formed in the front surface of the movable frame 4 in the side opposite to the first coil 4 b. The first coil 4 b and the first magnetic material 5 b are not in contact with each other. Further, the hall element 106 for detecting the position of the movable frame 4 in the X-axis direction is fixed to the movable frame 4. The hall element 106 is provided in the center of the coil 4 b.

As shown in FIG. 10, the first magnetic material 5 b is extended in the X-axis direction, and extends in the direction in which the magnetic poles of the opposed magnet 2 b are arrayed. Thus, the magnetic attraction force F in the direction denoted by an arrow F in FIG. 11 or, namely, the direction towards the first magnet 2 b acts on the first magnetic material 5 b opposed to the first magnet 2 b and fixed to the movable frame 4. This magnetic attraction force F acts on the movable frame 4 holding the first magnetic material 5 b, and becomes a force holding the movable frame 4 in a direction towards the fixed frame 2.

Next, with reference to FIGS. 12, 13, 14, 15, 16, 17, 18, and 19, a description will be made of a relationship between strength of magnetic springs and the shape of the first magnetic material 5 b (including the layout of the first magnetic material 5 b). The description below also pays attention to the magnetic spring including the first magnetic material 5 b. Needless to say, however, the same description applies to the other magnetic springs.

FIG. 12A is a front view showing a relationship between the first magnet 2 b and the first coil 4 b. FIG. 12B is a side view thereof. The first magnet 2 b is fixed to the fixed frame 2, and the first coil 4 b is fixed to the movable frame 4. There is a gap between both the magnet and the coil. When a control current flows through the first coil 4 b, the movable frame 4 (not shown here) comprising the first coil 4 b is moved in an array direction of magnetic poles in relation to the fixed frame 2 (not shown here) comprising the first magnet 2 b. Hereinafter, this direction will be referred to as a driving direction. Further, a direction perpendicular to the driving direction will be referred to as a cross-driving direction.

Intensity distribution (profile) of magnetic flux in the front side of the first magnet 2 b or, namely, in the side in which the first coil 4 b and the first magnetic material 5 b are arranged varies between the driving direction and the cross-driving direction. As is known from the intensity distribution of the magnetic flux along the driving direction, the direction of the magnetic flux is inverted at a branching position of the two poles and the intensity is found to change greatly, as shown in FIG. 13. On the other hand, as is known from the intensity distribution of the magnetic flux along the cross-driving direction, there is substantially no change as a constant intensity is exerted, as shown in FIG. 14.

The first magnetic material 5 b according to the present embodiment is extended in the driving direction, opposed to the first magnet 2 b, and is therefore easily influenced by the intensity distribution shown in FIG. 13. As has been described above, the direction of the magnetic flux of the first magnet 2 b is inverted along the array direction of the magnetic poles thereof. Therefore, the first magnetic material 5 b extended in the driving direction and opposed to the first magnet 2 b is also magnetized by the poles opposite to the poles of the opposed first magnet 2 b, as shown in FIGS. 15 and 16.

At this time, if the lengths of areas of the first magnetic material 5 b which are opposed to the two magnetic poles of the first magnet 2 b are equal to each other, as shown in FIG. 15, i.e., if the lengths of areas where the first magnetic material 5 b is opposed to the magnetic poles of the first magnet 2 b are equal to each other, the exact center of the first magnet 5 b is a boundary of magnetized magnetic poles, and magnetic forces are maintained balanced. That is, in this case, the force acting on the first magnetic material 5 b is substantially only the magnetic attraction force F in a direction toward the first magnet 2 b, and a force acting in the driving direction is not generated.

In contrast, when the first magnetic material 5 b moves in the driving direction in relation to the first magnet 2 b, as shown in FIG. 16, the area size of the first magnetic material 5 b which is magnetized changes, and the magnetic force is unbalanced. For example, when the first magnetic material 5 b shifts leftward in the figure in relation to the first magnet 2 b, as shown in the figure, the left area of the first magnetic material 5 b which is opposed to the S-pole in the left side of the first magnet 2 b in the figure is magnetized to the N-pole. The length of this area accordingly increases to be greater than the other area in the right side which is magnetized to the S-pole. In this case, a force to return in the direction of maintaining the balance of the magnetic force (i.e., the rightward direction in the figure) acts on the magnetic material 5 b. That is, this force turns into the restoring force R in the driving direction along the XY-plane of the magnetic spring.

From a different viewpoint, the restoring force R in the driving direction serves as a load at the time of driving the movable part 4. That is, if the restoring force R in the driving direction is intensified excessively, the power consumption of the VCMs increases and the operating time of a battery shortens. On the other hand, when a coil spring is used, the spring needs to be long in order to reduce the restoring force to suppress power consumption because the restoring force in the driving direction is proportional to a spring constant. Consequently, the installation space thereof increases.

Further, as a matter of course, there is an appropriate value for the magnetic attraction force F in the direction of attracting the first magnetic material 5 b to the first magnet 2 b. If the magnetic attraction force F is too small, driving of the movable part 4 becomes unstable. Conversely, if the magnetic attraction force F is too great, a problem of abrasion occurs due to the balls 3 a, 3 b, and 3 c. Therefore, when a magnetic spring is used as in the present embodiment, the intensity of a spring or, namely, the magnetic attraction force F and the restoring force R are desirably designed to be appropriate values.

FIG. 17 is a graph which shows a relationship between the movement of the magnetic spring along the driving direction of the first magnetic material 5 b and the restoring force R thereof along the driving direction, according to the present embodiment. For comparison, another relationship is shown between a shift amount of a coil spring along an XY-plane thereof and restoring force thereof along a plane direction thereof, where the coil spring generates an attraction force of the same size as the magnetic attraction force F of the magnetic spring as described above. According to this graph, the restoring force of the coil spring is found to be higher by 80 to 90% than the restoring force of the magnetic spring. That is, the restoring force can be reduced to be comparatively small by using a magnetic spring.

According to the present embodiment, in addition to use of characteristics of a magnetic spring as described above, the magnetic attraction force F of the magnetic spring is controlled to a value, separately from the restoring force R of the magnetic spring.

Basically, the first magnetic material 5 b needs to be long along the driving direction to some extent, in order to make the restoring force R described above act on the magnetic material 5 b. In this sense, if the first elongated narrow magnetic material 5 b is extended in the cross-driving direction along the polarization line D of the first magnet 2 b, the restoring force in the driving direction cannot substantially be made to act on the magnetic material 5 b.

As shown in FIG. 18, the lengths of the S-pole and the N pole of the first magnet 2 b along the array direction thereof are expressed as L_(S) and L_(N), respectively. Where a movement amount of the movable part 4 holding the first magnetic material 5 b is supposed not to exceed the length L_(S) (L_(N)) of each of the poles, the length L of the first magnetic material 5 b along the driving direction need only be longer than the length L_(S) (L_(N)) of the corresponding pole. In other words, the lower limit of the length of the first magnetic material 5 b need only be such a length that causes at least part of the first magnetic material 5 b to overlap the polarization line D of the first magnet 2 b when the movable part 4 moves in relation to the fixed frame 2. The polarization line D represents a virtual line which expresses a boundary between the S-pole and the N-pole.

On the other hand, the magnetic attraction force F which acts on the first magnetic material 5 b changes in accordance with the projection area of the first magnet 5 b on the first magnet 2 b, i.e., the length L and the width W of the first magnetic material 5 b, the thickness H of the first magnetic material 5 b along the direction of optical-axis O (refer to FIG. 19), and the distance from the first magnetic material 5 b to the first magnet 2 b. In other words, the magnetic attraction force F acting on the first magnetic material 5 b can be controlled to a desired value by adjusting at least one of the dimensions (L, W, H) of the first magnetic material 5 b and the distance thereof to the first magnet 2 b.

That is, according to the present embodiment, after setting the restoring force R of a magnetic spring to an appropriate value, the magnetic attraction force F of the magnetic spring can be set to a desired value, irrespective of the restoring force R. Accordingly, efficient and stable blur correction operation can be achieved.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.

For example, the foregoing embodiments have been described with respect to a case that the magnets 2 a, 2 b, and 2 c are provided on the fixed frame 2 and the magnetic materials 5 a, 5 b, and 5 c are provided on the movable frame 4. However, the present invention is applicable also to a vibration-proof unit of a moving magnet type in which magnets 2 a, 2 b, and 2 c are provided on a movable frame 4, as in a modification shown in FIG. 20. Also in this case, a magnetic attraction force of a corresponding magnetic spring can be controlled to a desired value by changing the dimensions of magnetic materials 5 a, 5 b, and 5 c fixed to a fixed frame 2 and the distance between the magnetic materials 5 a, 5 b, and 5 c and the magnets 2 a, 2 b, and 2 c. 

The invention claimed is:
 1. A retention mechanism comprising: a fixed part; a movable part arranged to be movable in relation to the fixed part; a magnet provided on one of the fixed part and the movable part and having magnetic poles arrayed in a driving direction of the movable part; a coil provided on the other one of the fixed part and the movable part and arranged to be opposed to the magnet; and an elongated narrow magnetic material which is arranged to the other one of the fixed part and the movable part and is arranged to be opposed to the magnet with the coil inserted between the magnetic material and the magnet so as to form, in combination with the magnet, a magnetic spring, wherein the elongated narrow magnetic material is arranged so as to satisfy: (1) a condition that a longitudinal direction of the elongated narrow magnetic material is an array direction of magnetic poles of the magnet and is a direction along the driving direction of the movable part driven by the magnet and the coil; and (2) a condition that a length of the elongated narrow magnetic material along the longitudinal direction is longer than a width of the coil in the driving direction and is shorter than the width of the coil in a direction perpendicular to the driving direction.
 2. The retention mechanism according to claim 1, wherein the elongated narrow magnetic material is shorter than a width of the magnet in the driving direction of the movable part.
 3. The retention mechanism according to claim 2, wherein the elongated narrow magnetic material is positioned to be opposed to the magnet in a positional relationship in which area sizes of two areas of the elongated narrow magnetic material respectively projected onto the magnetic poles of the magnet are equal to each other.
 4. The retention mechanism according to claim 3, wherein the elongated narrow magnetic material has a size such that the area projected onto the magnet is inside an outer peripheral part of the magnet.
 5. The retention mechanism according to claim 4, wherein a length of the elongated narrow magnetic material along the longitudinal direction is longer than a length of each of the magnetic poles of the magnet along the longitudinal direction.
 6. The retention mechanism according to claim 1, wherein a magnetic attraction force between the elongated narrow magnetic material and the magnet is controlled by at least one of a size of an area of the elongated narrow magnetic material projected onto the magnet, a thickness of the elongated narrow magnetic material, and a distance between the elongated narrow magnetic material and the magnet.
 7. The retention mechanism according to claim 1, further comprising a detection member which detects a change in a magnetic force of the magnet and is arranged to the other one of the fixed part and the movable part, wherein the detection member is arranged to be opposed to a boundary between the magnetic poles of the magnet within a winding of the coil.
 8. A blur correction apparatus comprising: a fixed part; a movable part which holds an optical member as a target of a blur correction and is provided arrayed in a first direction along an optical axis of the optical member in relation to the fixed part; a plurality of rolling elements which are arranged between the fixed part and the movable part and support the movable part to be movable along a plane perpendicular to the first direction in relation to the fixed part; a first magnet provided on one of the fixed part and the movable part and having magnetic poles arrayed in a second direction perpendicular to the first direction; a first coil which is opposed to the first magnet and is provided on the other one of the fixed part and the movable part; a first magnetic material which is provided on the other one of the fixed part and the movable part, opposed to the first magnet so as to form in combination with the first magnet, a first magnetic spring, and is extended in the second direction in which the magnetic poles of the first magnet are arrayed; a second magnet provided on one of the fixed part and the movable part and having magnetic poles arrayed in a third direction perpendicular to the first direction and the second direction; a second coil which is opposed to the second magnet and is provided on the other one of the fixed part and the movable part; and a second magnetic material which is provided on the other one of the fixed part and the movable part, opposed to the second magnet so as to form, in combination with the second magnet, a second magnetic spring, and is extended in the third direction in which the magnetic poles of the second magnet are arrayed, wherein each of the first magnetic material and the second magnetic material is formed in an elongated narrow plate shape and is arranged so as to satisfy: (1) a condition that a longitudinal direction of each of the magnetic materials is an array direction of the magnetic poles of each of the magnets and is a direction along a driving direction, which is the second or the third direction, of the movable part driven by each of the magnets and each of the coils; and (2) a condition that a length of each of the magnetic materials along the longitudinal direction is longer than a width of each of the coils in the driving direction and is shorter than the width of each of the coils in a direction perpendicular to the driving direction.
 9. The blur correction apparatus according to claim 8, wherein the first magnetic material is an elongated narrow plate member extended in the second direction along the perpendicular plane, and the second magnetic material is an elongated narrow plate member extended in the third direction along the perpendicular plane.
 10. The blur correction apparatus according to claim 9, wherein the first magnetic material is positioned to be opposed to the first magnet in a positional relationship in which sizes of two areas of the first magnetic material respectively projected onto the magnetic poles of the first magnet are equal to each other, and the second magnetic material is positioned to be opposed to the second magnet in a positional relationship in which sizes of two areas of the second magnetic material respectively projected onto the magnetic poles of the second magnet are equal to each other.
 11. The blur correction apparatus according to claim 10, wherein the first magnetic material has a size such that the area projected onto the first magnet is arranged within an outer peripheral part of the first magnet, and the second magnetic material has a size such that the area projected onto the second magnet is arranged within an outer peripheral part of the second magnet.
 12. The blur correction apparatus according to claim 11, wherein a length of the first magnetic material along the second direction is longer than a length of each of the poles of the first magnet along the second direction, and a length of the second magnetic material along the third direction is longer than a length of each of the poles of the second magnet along the third direction.
 13. The blur correction apparatus according to claim 8, wherein a magnetic attraction force between the first magnetic material and the first magnet is controlled by adjusting at least one of a size of an area of the first magnetic material projected onto the first magnet, a thickness of the first magnetic material along the first direction, and a distance from the first magnetic material to the first magnet, and a magnetic attraction force between the second magnetic material and the second magnet is controlled by adjusting at least one of a size of an area of the second magnetic material projected onto the second magnet, a thickness of the second magnetic material along the first direction, and a distance from the second magnetic material to the second magnet.
 14. The blur correction apparatus according to claim 8, wherein the first magnetic material is provided on the movable part in an opposite side to the first magnet with the first coil inserted between the first magnet and the first magnetic material, and the second magnetic material is provided on the movable part in an opposite side to the second magnet with the second coil inserted between the second magnet and the second magnetic material.
 15. The blur correction apparatus according to claim 8, further comprising a first detection member and a second detection member which detect changes in magnetic forces of the first magnet and the second magnet, respectively, and are arranged to the other one of the fixed part and the movable part, wherein the first detection member and the second detection member are arranged to be opposed to boundaries between the magnetic poles of the magnets within windings of the first coil and the second coil, respectively.
 16. A retention mechanism comprising: a fixed part; a movable part arrayed to be opposed to the fixed part; a plurality of rolling elements which are arranged between the fixed part and the movable part and support the movable part to be movable in relation to the fixed part along a plane perpendicular to an array direction of the movable part in relation to the fixed part; a magnet provided on one of the fixed part and the movable part and having magnetic poles arrayed in a first direction perpendicular to the array direction; and a magnetic material which is provided on the other one of the fixed part and the movable part, and opposed to the magnet so as to form, in combination with the magnet, a magnetic spring, the magnetic material being extended in the first direction in which the magnetic poles of the magnet are arrayed; wherein the magnetic material forms an elongated narrow plate member which is extended in the first direction along the perpendicular plane; and wherein the plate member is a cuboid having a length of L, a width of W, and a thickness of H, the thickness being along the array direction of the movable part in relation to the fixed part.
 17. The retention mechanism according to claim 16, wherein the plate member made of the magnetic material has a size such that areas projected onto the magnet are inside an outer peripheral part of the magnet.
 18. The retention mechanism according to claim 17, wherein the plate member made of the magnetic material is positioned to be opposed to the magnet in a positional relationship in which area sizes of two areas of the magnetic material respectively projected onto the magnetic poles of the magnet are equal to each other.
 19. The retention mechanism according to claim 16, wherein the width W of the plate member is smaller than a width of the magnet in a driving direction of the movable part.
 20. The retention mechanism according to claim 16, wherein a magnetic attraction force between the plate member and the magnet is controlled by at least one of an area of the plate member made of the magnetic material projected onto the magnet, the thickness H of the plate member, and a distance between the plate member and the magnet. 